It is well known to make porous medical implants and there are numerous prior art proposals. For example, WO2007/051307 discloses porous medical implants made from polyetheretherketone and salt (e.g. sodium chloride) in a process wherein the ingredients are placed in a mould cavity, compressed and heated to melt the polyetheretherketone but not the salt and form a moulded part. After subsequent cooling to solidify the mixture, the moulded material is placed in a water bath at 100° C. to dissolve the salt from the moulded part and define a porous moulded part.
U.S. Pat. No. 5,969,020 discloses microporous polymeric foams and microtextured surfaces suitable for medical applications. In preparing the foams, an organic crystalline polymer is melted and combined with a selected solid crystalline fugitive compound to produce a substantially isotropic solution. The solution is cooled under controlled conditions, which foster solid-solid phase separation by the simultaneous crystallization of the fugitive compound and the polymer, to produce a foam precursor containing the solidified fugitive compound dispersed through a matrix of the organic polymer. Crystals of fugitive compound are then removed by solvent extraction and/or sublimation, or like process to produce microcellular foams having a continuous, open-cell structure.
In such porous materials, the fugitive material must be completely removed in an appropriate process to ensure the porous material is not contaminated with any potentially toxic agents prior to implantation. Complete removal can be difficult and, accordingly, there is a risk that levels of fugitive material may remain even after (attempted) removal.
In porous materials for medical implants, it is desirable to define a substantially fully interconnected network of voids, firstly to facilitate complete removal of a fugitive materials used in the preparation of the porous material and, secondly, to define a highly osseoconductive material.